During the moving of drums, canisters, and like containers of hazardous materials, it is imperative that such containers not be dropped or otherwise physically mishandled with the attendant potential of dispersal of the hazardous material. For example, canisters of radioactive waste must be safely inserted into, or removed from, vertically oriented storage vaults. These vaults are located in a floor of a storage building and covered with a removable hatch. The canisters are elongated sealed cylinders and often weigh several thousand pounds, e.g. 3,000 to 4,000. This moving of the canisters is accomplished through the use of a grapple suspended from an overhead crane such that the grapple can be indexed over a selected vault unit. The grapple releasably engages a knob-like projection, for example, on the top of the canister. Furthermore, the hatch to the vault weighs of the order of 15,000 pounds. This hatch, too, must be manipulated remotely with a grapple.
Grapples employed in the prior art have been of several types. For example, mechanical grapples utilizing a "scissors" principal have been employed. Fingers engage the under surface of the knob, and grasp the canister when tension is produced by the crane cable. The grapple disengages when this tension is removed. It will be recognized that extreme care must be exercised during the lowering of the canister to prevent inadvertent release of the canister as when the canister is misaligned with the vault, for example.
Other types of grapples utilize pneumatic and/or electrical operators to assure positive engagement of the grapple and the canister. Such grapples must have a "fail safe" capability to prevent inadvertent disengagement. Also, pneumatic and electric systems are subject to damage by high levels of radiation that may be present in the environment of a radioactive waste storage facility.
Accordingly, it is a principal object of the present invention to provide a grapple for moving heavy objects, the grapple adapted to release the object under controlled conditions.
It is another object to provide an all mechanical grapple system that is inert to effects of radiation such that the grapple system can be used for the moving of canisters of radioactive waste.
It is a further object to provide an all mechanical grapple system which does not release from an object unless the steps for release are repeated at least a second time to minimize inadvertent release.
It is also an object of the present invention to provide a grapple system having provisions for locking the same in a grasped position whereby release of an object is prevented until the locking feature is disengaged.
An additional object of the present invention is to provide a grapple unit having provisions to disassemble the lug fingers thereof for emergency disengagement.
Still another object of the present invention is to provide a grapple unit adapted for ready disassembly for the replacement of components as well as the decontamination of the unit should such operations be required.
These and other objects of the present invention will become apparent upon a consideration of the drawings referred to herebelow, and the full description of the invention.